(1) Field of the Invention
The present invention relates to a linear compressor used in an air conditioner and the like for reciprocating a piston in a cylinder by a linear motor to compress gas, and more particularly, to a linear compressor in which a load is not applied, almost at all, to a direction perpendicular to a reciprocating direction of a piston.
(2) Description of the Prior Art
In refrigeration cycle, HCFC refrigerants such as R22 are stable compound and decompose the ozone layer. In recent years, HFC refrigerants begin to be utilized as alternative refrigerants of HCFCs, but these HFC refrigerants have the nature for facilitating the global warming. Therefore, a study is started to employ HC refrigerants which do not decompose the ozone layer or largely affect the global warming. However, since this HC refrigerant is flammable, it is necessary to prevent explosion or ignition so as to ensure the safety. For this purpose, it is required to reduce the amount of refrigerant to be used as small as possible. On the other hand, the HC refrigerant itself does not have lubricity and is easily melted into lubricant. For these reasons, when the HC refrigerant is used, an oilless or oil-poor compressor is required. A linear compressor in which a load applied in a direction perpendicular to an axis of its piston is small and a sliding surface pressure is small is known as a compressor which can easily realize oilless as compared with a reciprocal type compressor, a rotary compressor and a scroll compressor.
However, the linear motor used for the linear compressor has such a loss of end effect that if the piston receives a gas pressure which is being compressed, the axial length center of the moving member is deviated from the axial length center of the stator, and the thrust is lowered. If the displacement amount is further increased, a behavior of the moving member becomes unstable, and it is difficult to stably operate the linear motor.
Thereupon, it is an object of the present invention to provide an efficient and reliable linear compressor in which an axial length center of the moving member connected to a piston is previously deviated toward a compression chamber with respect to an axial length center of the stator, the axial length center of the moving member and the axial length center of the stator are substantially aligned with each other at the time of operation of the linear compressor.
It is another object of the invention to provide a reliable linear compressor in which a DC bias current is fed to a linear motor, thereby substantially aligning the axial length center of the moving member and the axial length center of the stator of the linear motor with each other at the time of operation of the linear compressor.
According to a first aspect of the present invention, there is provided a linear compressor comprises a cylinder supported in a hermetic vessel by a support mechanism, a piston which is supported concentrically with the cylinder such that the piston can move in an axial direction of the cylinder, and which forms a compression chamber between the cylinder and the piston, a spring mechanism for applying an axial force to the piston, and a linear motor portion having a moving member connected to the piston through a holding member and a stator fixed to the cylinder to form a magnetic path between the stator and the moving member, the linear motor portion generating thrust for moving the piston in its axial direction, wherein the linear compressor further comprises aligning means for aligning an axial length center of the stator and an axial length center of the moving member with each other at the time of operation.
According to a second aspect of the invention, in the linear compressor of the first aspect, the aligning means deviates the axial length center of the moving member toward the compression chamber with respect to the axial length center of the stator in expectation of a length through which the axial length center of the stator is displaced with respect to the axial length center of the moving member at the time of operation, and mounts the moving member thereon.
According to a third aspect of the invention, in the linear compressor of the second aspect, the length to be displaced is determined by a pressure fluctuation of a refrigerant gas in the compression chamber.
According to a fourth aspect of the invention, in the linear compressor of the second aspect, the length to be displaced is determined by a pressure difference between a suction pressure and a discharge pressure.
According to a fifth aspect of the invention, in the linear compressor of the first aspect, the aligning means feeds a DC bias current to the linear motor portion so that the spring mechanism receives a gas pressure to act against a displacing force of the spring mechanism.
According to a sixth aspect of the invention, in the linear compressor of the fifth aspect, the DC bias current is fed in proportion to a pressure difference between the suction pressure and the discharge pressure.
According to a seventh aspect of the invention, in the linear compressor of the fourth or sixth aspect, the suction pressure is defined as a suction pressure of a predetermined cooling condition or heating condition, and the discharge pressure is defined as a discharge pressure of a predetermined cooling condition or heating condition.
According to an eighth aspect of the invention, in the linear compressor of the fourth or sixth aspect, the suction pressure is defined as an average suction pressure between a suction pressure of a predetermined cooling condition and a suction pressure of a predetermined heating condition, and the discharge pressure is defined as an average discharge pressure between a discharge pressure of a predetermined cooling condition and a discharge pressure of a predetermined heating condition.
According to a ninth aspect of the invention, in the linear compressor of the seventh or eighth aspect, the predetermined cooling condition is set to an indoor set temperature of 27xc2x0 C. and an outdoor temperature of 35xc2x0 C., and the predetermined heating condition is set to an indoor set temperature of 20xc2x0 C. and an outdoor temperature of 7xc2x0 C.
According to a tenth aspect of the invention, there is provided a linear compressor comprises a cylinder supported in a hermetic vessel by a support mechanism, a piston which is supported concentrically with the cylinder such that the piston can move in an axial direction of the cylinder, and which forms a compression chamber between the cylinder and the piston, a spring mechanism for applying an axial force to the piston, and a linear motor portion having a moving member connected to the piston through a holding member and a stator fixed to the cylinder to form a magnetic path between the stator and the moving member, the linear motor portion generating thrust for moving the piston in its axial direction, wherein the linear compressor further comprises a position sensor for detecting a displacement of the axial length center of the moving member caused by a gas pressure.
According to a first aspect of the present invention, since the linear compressor comprises the aligning means which aligns the axial length center of the moving member with the axial length center of the stator during operation, even if the compressed gas force during operation is applied to the piston and the amplitude center of the piston is moved in a direction opposite from the compression chamber, the axial length center of the moving member and the axial length center of the stator are not largely deviated from each other and thus, the linear compressor can be driven efficiently.
According to a second aspect of the invention, in the linear compressor of the first aspect, the aligning means deviates the axial length center of the moving member toward the compression chamber with respect to the axial length center of the stator in expectation of a length through which the axial length center of the stator is displaced with respect to the axial length center of the moving member at the time of operation, and mounts the moving member thereon. With this design, the displacement can reliably be corrected, and the efficiency of the linear motor can be enhanced.
According to a third aspect of the invention, in the linear compressor of the second aspect, since a length to be displaced is determined by a pressure fluctuation of the refrigerant gas in the compression chamber, high performance can always maintained without lowering efficiency of the linear motor at the time of operation of the piston.
According to a fourth aspect of the invention, in the linear compressor of the second aspect, since the length to be displaces is determined by a difference between the suction pressure and the discharge pressure, it is possible to enhance the efficiency of the linear motor.
According to a fifth aspect of the invention, in the linear compressor of the first aspect, since the aligning means feeds a DC bias current to the linear motor portion so that the spring mechanism receives a gas pressure to act against a force which replaces the spring mechanism, the actuation of the moving member of the linear compressor is stabilized. Further, since the suction pressure oscillates in the vicinity of the neutral point, it is possible to reduce the necessary amplitude amount, and to enhance the reliability of the spring.
According to a sixth aspect of the invention, in the linear compressor of the fifth aspect, since the DC bias current is fed in proportion to a difference between the suction pressure and the discharge pressure, it is possible to precisely align the axial length center of the moving member with the axial length center of the stator and thus, it is possible to operate the moving member more stably.
According to a seventh aspect of the invention, in the linear compressor of the fourth or sixth aspect, since the suction pressure is defined as a suction pressure of the predetermined cooling condition or heating condition, and since the discharge pressure is defined as the predetermined cooling condition or heating condition, the piston receives the difference pressure between the suction pressure and the discharge pressure, and the displacement amount of the axial length center of the moving member is determined as an amount to be displaced previously, it is possible to substantially align the axial length center of the moving member with the axial length center of the stator, it is possible to enhance the efficiency of the air conditioner at the time of cooling or heating during operation.
According to an eighth aspect of the invention, in the linear compressor of the fourth or sixth aspect, the suction pressure is defined as an average suction pressure between a suction pressure of a predetermined cooling condition and a suction pressure of a predetermined heating condition, and the discharge pressure is defined as an average discharge pressure between a discharge pressure of a predetermined cooling condition and a discharge pressure of a predetermined heating condition. Therefore, a deviation amount between the axial length center of the stator and the axial length center of the moving member at the time of cooling and heating is reduced, the linear motor can be actuated efficiently, and it is possible to realize an air conditioner having high seasonal energy efficiency ratio.
According to a ninth aspect of the invention, in the linear compressor of the seventh or eighth aspect, the predetermined cooling condition is set to an indoor set temperature of 27xc2x0 C. and an outdoor temperature of 35xc2x0 C., and the predetermined heating condition is set to an indoor set temperature of 20xc2x0 C. and an outdoor temperature of 7xc2x0 C. Therefore, it is possible to reduce, during a year, a displacement amount between the axial length center of the stator and the axial length center of the moving member at the time of cooling and heating and thus, it is possible to operate the air conditioner in each mode, and to reduce power consumption to a low level.
According to a tenth aspect of the invention, a deviation of the axial length center of the moving member with respect to the axial length center of the stator, i.e., displacement of the spring mechanism is detected by a position sensor, and a DC bias current value is determined based on a detection signal of the position sensor. With this, the axial length center of the moving member which is deviated upon reception of a gas pressure during operation can precisely be aligned with the axial length center of the stator. Therefore, it is possible to stably operate the moving member of the linear compressor, and to enhance the reliability.